Voltage security assessment and control in electric power systems
This research addresses two aspects of voltage security in electric transmission systems. First, the efficient assessment of steady state security with respect to all plausible single and double line contingencies is investigated. Second, detection and avoidance of a dynamic voltage collapse event is investigated.This dissertation develops an expert system called SEEKS which assesses steady state voltage security by intelligently select line outages likely to cause steady state voltage violations. Outages are assessed in the context of the local topology and operating condition, using heuristics derived from operational planning experience. Information about topology is captured by grouping buses into neighborhoods (or structures), useful for comparing the impact of outages connected to the same structure. Using operational planning concepts, SEEKS tries to identify only the most severe outage amongst sets of outages in the same neighborhood. This assumes that remedial control used to compensate for the most severe outage will correct the violations caused by other outages in the same neighborhood.The worst outages are evaluated by running fast decoupled power flows. When voltage violations are found, remedial action consisting of capacitor, transformer, and generator adjustments is investigated. The results provide a sufficient but non-optimal set of controls for removing violations.This dissertation also develops an algorithm for local detection and remedial control of an imminent voltage collapse in real-time. The detection scheme monitors each load bus voltage and reactive load demand in the time domain, looking for an indication of imminent collapse at each bus. Once a collapse is detected at a bus, the remedial control scheme calculates the amount of control necessary to steer the system voltages away from the collapse.Imminent collapse is monitored by using continuously updated Thevenin equivalents at each load bus. The stability of the first order system consisting of the load bus reactive demand and the equivalent is continuously evaluated. When this system approaches instability, the remedial control scheme is triggered. The remedial control set consists of switchable capacitors and load shedding. The remedial scheme attempts to minimize both the load shedding and the total amount of control applied by iteratively applying remedial control.
- Electrical engineering